1. Field of the Invention
This invention relates generally to telecommunications systems, and more particularly to an apparatus that utilizes a standard television set for displaying information including information sent over a telephone subscriber loop.
2. Description of Related Art
A telecommunication device known as a telecommunications device for the deaf (TDD) enables the hearing impaired to communicate over regular telephone subscriber loops. The most common TDD includes a keyboard for typing outgoing messages, a modem (modulator/demodulator) for converting incoming and outgoing messages to signals which can be transceived over the subscriber loop, and a display CRT screen or printer for displaying the messages. While this type of TDD has been used for a number of years, it is accompanied by a number of limitations.
One limitation is the amount of components and cost required to construct such a device. Another limitation is that a non-audio indicator is needed to indicate an incoming call. This typically is accomplished by adapting the TDD to flash a room lamp in response to an incoming call. Moreover, while some TDDs include a printer for recording a message, most TDDs which encode messages in Baudot, ASCII, or CCITT formats, cannot utilize conventional answering devices.
It is known that many television channels include digital information for the purpose of closed captioning. Closed captioning is a means for transmitting hidden digital data in the unused portions of the television signal. The information is inserted in digital form onto unused lines, the so-called vertical blanking interval (VBI) portion of the television picture. On the receiving end, a decoder extracts the digital information and reintegrates it with the regular video signal for display on the television screen. The television receiver thus acts as a display terminal which converts digital information into text for display on the television screen.
One known format for closed-captioning is the Teletext system. The Teletext system authorized by the Federal Communication Commission (FCC) defines the data as being imbedded in lines 10 through 18 of the VBI with the transmission rate being dependent upon the number of lines used to transmit the data. Teletext systems are available which send an endless loop data corresponding to magazines, books, electronic yellow pages and the like. Provisions can be made to store a portion of this data in a personal computer for later review. The Teletext system, while being accepted in the European communities, never gained popularity in the United States due to the transmission complexity and the requirement that it be adapted to NTSC standards. Furthermore, the Teletext system does not provide color text, alternative text placement, or support multiple languages.
A new closed captioning specification (FCC 15.119), herein incorporated by reference, has been proposed by the Electronic Industry Association which utilizes the vertical blanking interval wherein captions associated with the television program are encoded into the composite video signal during line 21 of field one of the standard NTSC video signal. The proposed system further provides for color text and includes control information which provides instructions for the display format as well as the characters to be displayed.
While this new format is certainly useful to the hearing impaired, it also has benefits in instructional applications where reliance on the spoken word is not desired. One such example would be to teach or improve the context in which language is used or to improve reading capabilities.
Up until now, these seemingly unrelated technologies have not taken advantage of the substantial overlap between TDD and closed captioning and the benefits from joining the two together. It can be seen then that an apparatus which provides both TDD services and closed-captioning in a standard television receiver would provide a convenient platform for the hearing impaired to communicate as well as provide a benefit to society as a whole.